The movements of limbs, tissues and organs in medicine, physiological research, sleep research, ergonomics measurements for occupational physiology, etc may be measured using several methods. The most frequently used methods include strain, force and acceleration gauges, measurement of the electrical activity produced by the tissues (e.g. muscle electrical activity=electromyography=EMG) or measurement of changes in tissue movements or in properties of some materials affected by movements of the tissues (e.g. airflow caused by respiratory movements, changes in flow rate or temperature of the airflow). The measurement equipment is either fixed to the patient (e.g. strain gauge for changes in shape of the tissue) or he may be lying on a plate-shaped movement sensor (‘sleep research mattress’).
The measurements of movements caused by e.g. limbs or breathing (respiratory movements) are required in diagnostic studies and in the research of sleep disorders. Abnormal movement patterns (e.g. restless-legs syndrome, periodic movements of legs, see also the paragraph below) and pauses or lack of movements (e.g. pauses or irregularities of movements in otherwise regular breathing movements, i.e. apneas) are especially important for the diagnosis of sleep disorders. Concerning both adults and children, the number and distribution of movements are analyzed for the follow-ups of insomnia, poor/restless sleep, and daytime activity, for example.
One of the most common organic sleep disturbances is the ‘restless legs-syndrome’ (RLS) associated with repetitive periodic movements of legs and feet. Some patients know that they move their legs but other patients are not aware of it. If medical treatment is to be started the diagnosis of the disorder in question should be completed first. The diagnosis of the syndrome is determined utilizing a sleep recording called polysomnography. In this recording breathing and leg movements are typically studied using muscle electric activity pattern (EMG) with the measuring electrodes positioned on the legs (skin) during the sleep. The EMG signal is amplified and stored in the measurement equipment. The pauses in breathing, i.e. respiration, during sleep (˜sleep apneas) are another important application of sleep recordings. The respiratory movements are followed by e.g. strain gauges in addition to the simultaneous measurement of amount and fluctuation of airflow using pressure and temperature sensors. The movements of the limbs may be followed also in the daytime using e.g. an acceleration sensor called actography, resembling a watch attached to the wrist of the subject. The distribution of movements is used to evaluate the periods when the subject was active or stationary/not moving and especially when he was laying and sleeping, which typically occurs during the night. The aforementioned phenomena should be measured with as little disturbance to the subject's sleep and sleeping position as possible. Maximally small and light measurement devices, sensors and systems are best suited to this task including the possible utilization in performing home recordings.
Disadvantageously the present recording devices have to be activated and partly fixed to the subject, e.g. a patient, by specially trained personnel in a hospital research unit using special straps, ergonomic tapes and glue-like paste. In some limited measurements the subject may take the devices and sensors home for the overnight study and return them immediately in the next morning to the hospital/unit where the measurement is completed by printing out the results from the devices. This laborious procedure always bears a risk of failure caused by some, even in principle somewhat minimal, external disturbances. Typically a plurality of measurement devices, in size of more than 10×10×2 cm, are required with even more than ten measurement sensors, in size of 1×1×1 cm, and the connecting electric wires. An electronic contact to the subject is frequently required setting additional requirements for the power supply and electronic safety. Therefore nowadays the measurements may often be possible only for a hospitalized patient sleeping in an “unfamiliar” environment, which also significantly increases the costs of the measurements.
The long duration of the recordings is an additional problem to overcome in achieving a successful result. One of the commonly used measurements (Sustained Immobility Test, SIT) takes one hour and all-night recordings with the subject lying on his bed take between 6 and 12 hours. The relatively long duration of the recordings makes all the aforesaid problems of the presently used methods even more complicated. The storage and analysis of the huge amount of signals and data from the long-term or overnight measurements is a demanding task. After completing the measurements and starting the required treatments, the effect of medication is determined using repeated measurements that are especially required in the long-term use and follow-up of treatments. The repeated measurements multiply the problems listed above.
One example of a prior art solution is disclosed in publication US2003/0236474 setting forth an arrangement for monitoring movements of a patient via various sensors in order to detect seizure conditions during periods of sleep, for example. A detector assembly comprising both a conditioning circuit for filtering/amplifying the input measurement signal from the sensing devices and a peak detectors circuit for low-pass filtering the signal and periodically detecting peaks therein is presented. The peak voltages are conveyed via an A/D converter into a microcontroller that then determinates the nature of the related movements on the basis thereof. The peak signals are, first of all, compared with threshold values in order to detect the patient's movement; the detected movements (e.g. seizure intervals) are recorded in a non-volatile memory for a period of time. The sensing devices may include among a number of options a sound detector that is optionally attached to a blanket, a quilt etc made of special material to amplify the movement-originated noise and thus ease the detection thereof.
Prior art solutions, in addition to the complexity of the arrangements, also commonly concentrate on the threshold-based analysis of the measurement signals as a result of which only detection pulses/periods comprising activity as determined by the threshold-criteria set are stored for further processing/analysis. Such approach requires using tailor-made, sophisticated, expensive, and well-calibrated (even case-specifically) measurement equipment to avoid conducting similarly awkward re-measurements due to bad calibration, for example.
Further, the diagnostics and treatment of sleep disorders is laborious, expensive and difficult. Some more practical measurement methods are being developed but all the present equipment in routine use costs several thousands of euros per piece.
The need for measurements is universal. The most common organic sleep disorders are snoring, breathing pauses during sleep (sleep apnea) and restless legs syndrome with periodic leg movements during sleep. The frequency of these disorders is between 5 and 10 percent of the adult population and even higher among the elderly. All patients with such disorders cannot be examined in the hospitals or research units, and a screening possibility is required too. The screening is performed exploiting the symptoms detected by the patient. The abnormalities during sleep are, however, quite difficult to recognize unless e.g. some other member of the patient's family has not detected the symptoms. The patients themselves may not be aware that they have a disorder with a potentially curable treatment. There fortunately still are several treatments available: treatment of sleep breathing problems like apneas with snoring operations, ventilation assisting devices and weight lose, treatment of insomnia with sleeping pills, and especially new drugs for restless legs syndrome. Nevertheless, for the restless legs syndrome there is a particularly great demand for new methods suitable for the diagnosis and follow-up of the effects of the treatment.